Telephone system



Jan. 12, 1943. o. A. PEARCE l 2,307,855

TELEPHONE SYSTEM Filed May 5, 1941 n 'l FSM fs sheets-sheet 1 Q MTR W. QJJJJ( y U Q 21a? n E cZ L S5 Ll f A'TT'OREY `lan. 12, 1943. o. A. PEARCE 2,307,855-

TELEPHONE SYSTEM Filed may s, 1941 s sheets-sheet 2 INVENTOR OWEN Avls Pz-:ARCE

'Y TTORNEY M512, 1943?. o. A. 15x-:ARCE 2,307,855

TELEPHONE SYSTEM y i Filed May s, 1941 3 sheets-sheet 5 INVENTOR I OWEN AVIS PEARCE ATTORNEY Steps Patented `ian. i2, i943 S'E'AS TELEPHONE SYSTEM Application May 3, 1941, Serial No. 391,643 In Great Britain June 22, 1940 16 claims.

The present invention relates to telephone systems and is more particularly concerned with systems in which a group of subscribers is served for both incoming and outgoing calls by a single two-conductor line extending to the exchange. The chief object of the invention is to provide an improved multi-party line system of this type in Which improved arrangements are made to maintain and to supervise the service to the group of subscribers involved.

According to one feature of the invention, in a telephone system including party lines arranged so that only one party at a time can connect his equipment to the line, each subscribers equipment includes a device adapted to be operated in response to a controlling action at the exchange to disconnect the said equipment from the line.

According to another feature of the invention, in a telephone system including party lines arranged so that the connection of any subscribers equipment to the line for either an incoming or an outgoing call is dependent upon the transmission of impulses from the exchange, the impulses also serve to effect the stepping of a switch at the exchange the circuit for bringing this switch to rest when the required number of impulses have been transmitted extending over a wiper of the switch to enable a portion to be individual to the various stations so that service to particular stations may be denied by interrupting the corresponding individual portion.

According to a further feature of the invention, in a telephone system including party lines arranged so that the connection of any subscribers equipment to the line for either an incoming or an outgoing call is dependent upon the transmission of impulses from the exchange, if the line is looped due to a fault, the impulse responsive switches at the substations are set to a characteristic position in which no station is connected up and a switch in the exchange which in synchronism with the substation switches is set to a corresponding position in which it initiates the giving yof an alarm.

The invention will be be better understood from the following description of one method of carrying it into effect, reference being had to the accompanying drawings comprising Figs. 1-3. These should be arranged side by side with Fig. 1 on the left to form a circuit diagram of the switching unit required at the main exchange per party line group and of the equipment required at Jthe station of one subscriber in the group.

It will be seen that one two-conductor line extending from the exchange is provided per group of subscribers, the apparatus required individual to each subscriber in the group being connected across the line as shown in Fig. 3 which discloses the equipment of only one of the subscribers, for instance subscriber No. 4.

Each party line groupis assumed to comprise up to ten subscribers, each of which requires apparatus including two neon tube gas discharge devices NTA and N'I'B, two step-by-step electromagnetically-operated 12-position switches F and C and a relay PGR which is provided with a mechanical latch so that it will lock in its operated position. Assuming the main exchange is automatic, each subscriber will also be provided with an automatic telephone instrument the circuit of which is also shown in Fig. 3.

At the main exchange each party line group is provided with a switching unit, the circuits of which are shown in Figs. 1 and 2, which unit is introduced between the party line and the usual line and cut-01T relay assembly and includes a 25-position reverse-drive electromagneticallyoperated stepping switch which serves to count or control the impulses transmitted on calls between the main exchange and the group of subscribers.

It will be appreciated that in addition to the facilities 'already mentioned, the party line system to be described is suitable for use in connection with either a manual or an automatic exchange, provides secrecy of communication and quality of transmission substantially equal to that of ordinary individual line subscribers, and gives individual metering of outgoing calls. Provision is also made for local intercommunication between the subscribers of a group. The general arrangements are similar to those of the system disclosed in United States Patent No. 2,180,963.

Before consideration is given to the circuit operations consequent on the initiation or recep- -tion of a call by a party line subscriber, reference Will be made to the switches F and C" which are provided at the station of each subscriber in the group. Of the twelve positions provided thereon, the rst is the home position, the second is utilised under line fault conditions as will be seen later and of the other ten positions a different position is allocated to each subscriber. Two cams are mounted on the driving shaft of each switch, one of which serves to operate oli-` normal springs when the switch steps from the home position, while the other cam is arranged to operate other springs in the particular position of the switch characteristic of the subscriber concerned. Thus the switches associated with No. 1 subscriber will operate these springs in position 3 only, while the simtches associated with No. 2 subscriber will operate these springs in position 4 only, and so on up to position 12 for No. 8 subscriber.

When one of the subscribers initiates a call by removing his receiver, the switch hook contacts SHI complete a loop across the negative and positive leads to the main exchange. A circuit is then completed from earth, wiper SI, Fig. 2 in position 1, armatures 0113 and ic3, left-hand high resistance winding of relay ST, armatures rfi, sr3, pg2, to2, M3 and ctll, negative conductor of the party line, armature pgrl in the calling station, off-normal contacts F(N) of switch off-normal contacts C(N)2 of switch C, rectifier MRE in a conductive direction, winding of relay PGR, contacts SHI, resistance I8, positive line, armatures ct, pri, sl, f2, pgS, right-hand winding of relay RF to battery. Only relay ST operates in this circuit and locks up over its make rst armature stI and its right-hand winding, and at armature $152 operates relay ON, at armature sill busies the line to incoming calls and at armature S153, Fig. 1, applies earth to common lead I3 in order to start up a common pulse machine or pulsing relay, contacts of which will periodically loop the conductors I4 and I5, Fig. 2, at a rate of the order of three pulses per second. The first looping of leads I4 and I5 operates relay PGA from earth connected over armatures ctt, ce2, srl, on2, oni, and st2. This relay thereupon at arma-ture pgal prepares a circuit for relay PG which is short-circuited at this stage and at Varmature pga maintains an earth on start lead I3 independently of relay ST.- When v the connection between leads Ill and I5 is opened, the short-circuit is removed from relay PG which thereupon operates in series with relay PGA relay PR operates and at armature prI applies a high potential of the order of 100 volts negative to earth over common lead I2 and armatures 0T2, pri and cti to the positive line, at armature @r2 completes an energising circuit for the magnet SM of the switch S, and at armature w3, Fig. l, disconnects relay SZ from the negative line.

On the next opening of the pulsing contacts, relay PR releases and disconnects the high voltage pulse circuit and the circuit to the magnet SM whereupon the wipers of switch S are advanced to position 2. Succeeding pulses operate cn relay PR in the manner described and high potential pulses which are counted by switch S are transmitted to all the party line subscribers equipments in parallel.

In response to each pulse the neon tube NTA associated with each station in the group is caused to strike since the rectifier MRC in series therewith is in a conductive direction and current thereupon flows through the winding of each switch F which responds, the rectier mD in parallel therewith being non-conductive for current in thisdirection.

In response to the rst pulse received, each F switch advances from the home position 1 to position 2 in which position the oit-normal springs are operated and at contacts F(N)I remove rectiier MRD from across the magnet winding, while contacts F(N)2 disconnect the calling loop from across the line. At the same time contacts F(N)2 of other subscribers switches prevent them looping the line if they attempt to originate a call.

In'response to the second pulse the F switches are stepped to position 3 whereupon the contacts FI and F2 on the switch associated with subscriber No. 1 are operated. Assuming that this subscriber has not originated the call, no loop by way of his instrument will be connected across the line since hisk switch hook contacts are not operated and therefore the transmission orsetting pulses from the exchange will not be stopped.

If however subscriber No. i has originated the call, when all F switches are stepped to position 6 on receipt of the fth pulse from the main exchange, a loop will be connected across the line by way of contacts F2 of the -switch associated with subscriber No. 4, impulse springs of dial switch ID, telephone instrument, contacts FI, winding of relay PGR, contacts SHI,'resist ance IIJ to positive line. On the release of relay PR at the end of the fth pulse, relay SZ is reconnected to the negative line by armature m3 and it thereupon operates over the loop to the earth potential connected to the positive line over armatures ct, pri, srt, 1f2 and p93. Relay PGR still does not operate. Relay SZ at armature sel completes a locking circuit for itselfover wiper and bank S5 to battery connected to the negative line via thewinding of the line relay associated with the party line group, which relay now operates and at armature S22, Fig. 2, disconnects the earth feed to the impulsing` circuit for relay PR and releases relays PGA and .PG thereby stopping the transmission of pulses from the exchange to the party line. Relay ST will have released when the S switch advanced from the home position l, but relay ON remains held over the wiper and bank SI.

It will be understood that although all the subscribers F switches have been set in position 6, since only the F switch associated with No. 4 subscriber is arranged to operate its contacts FI and F2 in this position, only the telephone instrument of No. 4 subscriber in the group will be bridged across the line. In the main exchange the switch S which has been stepped in synchronism with the switches F will also be set in position 6 and in a manner to be'described serves to effect individual metering of outgoing calls on the automatic main exchange. In the case of a manual exchange it serves to indicate to the operator which subscriber in the group has originated the call.

For the purpose of the description the automatic main exchange is further assumed to be of a known type employing individual line switches and booster battery metering. Accordingly when relay SZ locks in series with the line relay, the operation of the latter will cause the rotary line switch to hunt for an idle rst selector. Relay CT is connected across leads M and MI in parallel with the cut-ofi` relay, lead MI extending to the battery side of the cut-off relay,

- and hence when this relay operates when an idle -nrst selector is found, relay CT is also operated. The cut-.off relay and relay CT .thereupon extend the negative and positive party line leads through to the rst selector in preparation for receiving dialled digits in accordance with the wanted number. Relay SZ is disconnected from the negative line at armature ctS and releases, and the impulse receivingrelay in the iirst selector is now operated from the calling partys loop. At armature .ct2 4battery is connected up over wiper and bank S3 to .the particular meter MTRI-MTRI Il associated with the calling party line subscriber, the meter -being in this case meter MTR4 which is .selected by wiper AS3 in position 6. This meter is now in readiness for being operated by booster battery metering potential which will be extended thereto over the M lead when the wanted party subsequently .answers after the dialled up connection has been extended through. Conversation now proceeds and it will be noted that .although relay PGR is. in circuit with the conversational path, a low impedance to speech currents is offered by the condenser QB bridged across it.

At the end of conversation when the calling subscriber hangs up, .the earth which holds the cut-off relay and relay CT is removed and lthese two relays now release. Relay CT at armatures e154 and ct5 prepares .for'the sending out of further high potential 'pulses to the party line and at armature ct re-completes the pulsing circuit for relay PR. Relays PGA and PG are operated as before and relay PR is then pulsed to extend further high potential negative pulses to the pcsitive line and at the same time to extend pulses f to the magnet SM of switch S.

AIn response to the application cf the high potential negative pulses, the F switches at the various party line stations are stepped in -synchronism until they again reach the home position I when the contacts F(N)-I and F(N)2 will be restored to normal. Rectier MRD will now be bridged across the winding of each F switch magnet and serves as a short-circuit during the break period between pulses, thereby holding the magnet operated to prevent the switches from being vstepped past this position. The total number of pulses transmitted is at least equal to the maximum number required to home the F switches from any position, and sending out of these pulses is terminated when the wiper SI reaches either of the homing positions 13 or l according to whether the switch is working over the rst or secon-d half of the bank. Relays ON, PGA, PG and PR now restore and the various F switch magnets of the parties also restore and all subscribers equipments and the main -exchange equipment is now normal in readiness for further calls.

Considering now an incoming call to one of the group subscribers, when the final selector selects the desired party, earth `is extended from the switching relay therein over a particular one of the private conductors PI-Pll, Fig. 2 in the nal selector multiple FSM according to the parl ticular party line subscriber being called, and this earth extends via bank and wiper S2 to operate relay IC.

The arrangement for the individual extension of the P conductors I-i associated with the wanted group via jack links ILI to ILI to relay IC is provided to enable any subscriber to be barred incoming service from the main exch-ange if this beso required, and this can be eifected by removal of the relevant link. The same re- .marks applyin. connection with outgoing calls where. by `removal of any one nf `the links OLI to OLII) outgoing service can be denied to the corresponding parties vsince if a subscriber with barred outgoing service .facilities attempts to originate an outgoing call, no circuit can be completed for relay SZ .to stop transmission of pulses when suiicient have been sent to set the F switches on to a position corresponding to the particular party involved. In these circumstances transmission is automatically stopped by the release of relay ON when the S switch reaches its home position at which time the F switches will again 'have reached their-normal l positions. I

Returning to the operation of 4relay IC in response toan incoming call, this .relay at armature icl locks `independently ofwiper S2, disconnects the normal connection of the left-hand winding of relay ST to the line at armature lz'c2, completes an operating circuit for relay ST by way of its right-hand winding at armature z'c3, and at armature iclI applies earth to the P lead extending to the line switch circuit so as tooperate the cut-olf relay therein and so prevent the line relay from being energised and initiating the operation of the line switch. 'Relay IC also at armature z'c prepares a circuit for relay CR and at armature ict disconnects any circuit for the meters M'IRI-M'IRIIl. Relay ST as before locks over its armature stl, operates relay ON over its armature str vand at armature sts applies earth to the pulse machine start lead I3. Relay ON connects earth over armatures str, onI, om, and c5 to operate relay CR which locks independently of relay IC `at its armature crI. Relay CR also at armature 0T2 connects up over common lead I I a source of high potential positive to earth to the armature prI and at armature cr3 connects up the lower winding of relay SZ to the positive party line conductor. Relay ON also at its armatures onl and 0112 extends earth to the pulsing circuit and relays PGA and PG operate as before, while relay PR is impulsed from the pulsing contacts connected to leads I4 and I5. At armature pri high potential positive pulses are now applied to the positive line, While at armature pf2 the switch magnet SM is operated in synchronism and the number of pulses applied to line will be adjusted as will be seen later in accordance with the particular subscriber required.

At the various stations the rectier MRC will now be non-conductive and rectifier MRB conductive to these pulses so that the C switches will now respond to the high potential pulses applied.

lConsidering now the impulse train in detail, the rst pulse transmitted steps both the S and C switches to position 2, while the next ten pulses step the C switches to the effective positions 3-12. The number ofpulses transmitted is determined by wiper and bank S4, Fig. 1, in accordance with the particular subscriber being called. For instance, if No. 4 subscriber is being called, after a total of five pulses have been transmitted when the S andC switches will occupy position 6, wiper Sil will encounter battery potential from the ringing return battery in the iinal selector which connects with contact 6 in the Sil bank Via No. 4. positive conductor -of the party line group in the fina-l selectormultiple. Relay SZ will thereupon operate over its lower winding and will stop the transmission of pulses as previously described. Relay SZ also operates relay CT as before since the cut-off relay is `operated and relay CT at ar- 'matures ctll andctli connects No.4 partyA line positive conductor in the final selector multiple and the negative conductor common to the party line group in the nal selector multiple through to the party 'linewhereupon ringing current is extended via kthe nal selector ring trip relay and out over the negative conductor of the party line.

vMeanwhile at the station of the wanted subscriber No. 4, contacts CI and C2 of the switch C "will have been operated on the positioning of this switch to position 6 and the earthed bell B of this subscriber is connected by way of normal contacts SH2, condenser QA and contacts C2 tothe negative line, so that this bell will ring.

When subscriber No. 4 removes his receiver, contacts SHI and SH2 operate to disconnect the bell and to connect a loop via the telephone' instrument across the line, thereby tripping the ringing. Conversation now proceeds.

At the conclusion of the conversation when the calling party hangs up, earth is removed from the nal selector P lead thereby releasing relay IC which in turn releases the cut-off relay in the line switch circuit and also relay CT. Relay SZ is also released on the release of the nal selector, 'and earth will therefore be extended over wiper and bank Si and armatures on2, srl, $22 and ct toV start up the pulsing circuitrelays once again.

A plurality of positive pulses is now transmitted over the positive line to home the C switches and the S switch is also horned and controls the number vof homing pulses sent out in the manner describedv previously in connection 4with the F switches, after which all equipment is restored to normal in readiness for subsequent calls.

Should a party line subscriber desire to call another subscriber on the same line, he first calls the exchange in the usual manner, whereupon all F switches are set to a position in accordance with the number of the particular subscriber calling, and the calling subscriber is connected up to a first selector. The dialling of the number of another subscriber on the sarne line then causes thercall to be extended to a revertive calling switch which is ysuitably set by further dialling. The calling subscriber now hangs up and it will be understood that the `revertive calling equipment now transmits the required number of positive pulses over the positive line 'to step all C switches to the position corresponding to the wanted party, the transmission being effected in a similar manner to that employed by the switching unit in the case of an incoming call to the party line. At the end of the positive pulse train,

the C switch associated with the wanted party closes its contactsCl and C2 and thereby connects his earthed bell to the negative line. It will be appreciated that the F switch associated with the calling subscriber will also have operated contacts FI and F2 and since his receiver is already restored, his bell also will be connected to the negative line. On the application of ringing current, the bells of both the -calling and called subscribers will thus be rung in parallel and when they reply, their telephones will be connected in parallel to the main exchange and conversation may proceed.

It will be noted that a resistance lil is included in the conversational circuit of each of the parties, and it will be understood that these resistances are adjusted so that the loop resistance offered by all parties approximates to 600 ohms .thereby ensuring that currents through the transmitters of the two parties under revertive call rconditions will be substantially equal.

On the completion of a conversation a series of high voltage positive pulses are first of all transmitted to line from the revertive relay set to home the C switches. The counting switch in the revertive relay set corresponding to the switch S in the switching unit shown on reaching its normal position causes the revertive relay set to drop out of the connection. Relay CT is thereupon released to initiate the sending out of a series of negative pulses to home the F switches in the same manner as described in connection with an outgoing call Ioriginated by a party line subscriber.

In case a party line subscriber should remove his receiver but omit to dial, the selector taken into use originates an alarm via suitable delayed alarm equipment. Arrangements are provided whereby the faulty station in question may be isolated or locked out from the common line in order that thi-s line may be restored to the service of the otherV stations thereon. For this purpose a key designated KPR is provided in the switching unit in the exchange and on being momentarily operated clears the faulty subscriber from the common line in the following manner. Ai contacts KPRI, Fig. 2, relay SR is operated, and this relay at armature ST2, Fig. 1, releases relay CT to clear the connection set up to the main exchange first selector.

On the release of the key, relay SR commences to release slowly, and during its release time high voltage positive to earth is fed over common lead Il, key contacts KPR2 and armatures 3T3, pc2, 02, prt and cfJ on to the negative line, while an earth potential is fed over contacts KPRl and armatures ST4, pri and ctB on to the positive'line. At the faulty substation the so-called permanent glow relay PGR is connected across the lineby way of resistance lLswitch hook contacts SPILwinding of relay PGR, F switch contacts Fl, telephone instrument, F switch contacts F2 to the negative line and relay PGR is thereupon operated. The neon tubes NTA and NTB do not tend to flash under this condition since they are short-circuited 'by the earth connected to the positive line at the main exchange. On operating, relay PGR mechanically locks in the operated position by means of a suitable latching arrangement and at armature pgrl opens the start loop circuit.

On the release of relay SR the high voltage positive pulse source and the earth return are disconnected from theline and at armature srl an operating circuit is recompleted for relays PGA and PG and for the pulsing relay PR so as to initiate the homing of the switch S and the sending out of high voltage negative pulses in the usual manner to home the F switches. After this normal homing operation has vbeen completed, the other nine parties on the line are now enabled to obtain service therefrom, but as regards the faulty party, it will be necessary for a maintenance ofcer to visit his premises and unlatch the relay before the service can be restored to him. Alternatively, it could be arranged that the relay PGR could be automatically unlatched as soon as the party replaced his receiver.

Considering now the arrangements for dealing with faults on the common party line, it is arranged that the party line stations will be isolated and that an alarm will be given in the case of a contact below a certain resistance value between the negative and positive conductors of the party line, and oi an .earth Yfault below a certain resistance value on either conductor of the party line.

In the first case relay S'I operates by way of its left-hand winding in a series with relay RF as in the case ofthe origination of a normal call and after the rst pulse has been transmitted to line, in response to which all F switches will be stepped oiT-normal, a loop condition will still obtain on the party line, which condition only obtains in the case of contact between the party line conductors. Relay SZ will Vtherefore operate to stop the pulse transmission in the usual manner and relay RF will be operated from earth, lower winding of relay SZ, armatures ciS, GT3 and sel, wiper S5 in position 2, .key contacts KRI, left-hand winding of relay RF to battery. Relay RF at armature 'rfi disconnects the left-hand winding of relay ST from the line in order to render ineffective the origination of calls by any of the lparty line subscribers, at armature N2 completesa vlocking circuit for itself over its right-hand winding to earth via the release key contacts KR2, at armature 1'13 completes a circuit to light the line fault lamp LFL, at armature rf applies earth to common lead i6 so as to set into operation suitable delayed alarm equipment which will give analarm after a predetermined period, and at armature H disconnects the incoming call circuit via relay IC.

In the case of a fault earth on the positive line, relay'RF is directly operated over its rightliand winding and thereupon functions as already described, while in the case of a fault the release key RT whereupon at contacts KRI and KRZ the circuits for both windings of relay RF are disconnected and this relay thereupon releases. Ii the equipment has been stepped oinormal it is then horned in the usual manner.

It will lbe understood that each of the various subscribers stations on the party line could be provided with an indicator by means of which a visual busy indication could be given whenever the line was engaged. It will be further noted that the earthed switching equipment associated with each subscriber is connected to the positive line by way of neon tubes which in their non-conductive state during speaking conditions serve to isolate this equipment from the line thereby preventing the standard of speech transmission from being lowered.

In case the switch S in the exchange switch unit is accidentally stepped off-normal, it will be seen that a homing circuit to drive it to one or other of its two home positions l or 13 is completed via wiper and bank Si, armature 0112, magnet interruptor contacts sm and magnet SM to battery.

I claim:

1. In a telephone system, a party line, each station on said line having certain equipment thereat normally disconnected from said line, a start circuit at each station over which calls from that at the calling station to said line without :con-

necting said equipment at ,the others of said stations to said zline, a device, means vforat times operating said device over said line and the equipment at said calling station While `said equipment is connected to said line, locking means associated with said device for thereafter maintaining the device operated, means operated after an Ainterval for disconnecting said equipment at said calling station from said line, and meansv controlled by said-device, if same was previously operated while said equipment Was connected to said line, forvdisabling the startcircuit at said calling station and maintaining the same disabled to prevent subsequent initiation of calls from that station.

2. 'In a telephone system, a party line, station on said 'line having certain equipment thereat normally disconnected from said line, a start circuit at each station over which calls from that station may be initiated, means responsive to the initiation of a call over the start circuit at'any of said stations for connecting said equipment at the calling station to said line without connecting said equipment at the others of said stations to said line, a device, means for at times operating said device over said line and the equipment at said calling station while -said equipment is connected to said line, locking means associated with said device for lthereafter maintaining the device operated, means for disabling the start circuits at all of said stations so long as said lequipment at said calling station remainsconnected to said line, meansoperated ed from said line, a device at each'station, means f responsive tothe initiation of a call over the start circuit at any station for connecting said other circuit at the calling station only to said line, thereby to render elective-the device at said calling station only, means at the exchange thereafter operated for signalling over said line to operate said eiective device, and means controlled by said device upon said operation to thereof disable said start circuit, thereby to prevent subsequent initiation of a call thereover.

4. In a telephone system, an exchange, a party line outgoing from said exchange, each station on said line having a start circuit'over which calls from-that station may be initiated and also having another circuit normally disconnected from said line, a'device at each station, means responsive to the initiation of a call over the start circuit at any station for disabling all of said start `circuits and connecting said other circuit at said calling station only to said line, said other circuitwhen connected to said line effective to render said device at the calling station only re" sponsive to signalling current of a certain character applied tosaid line, means at theexchange thereafter operated to apply signalling currents of said certain character to said .line to operate said responsive device, means controlled by said;

each

device at said calling station upon said operation thereof to disable, independently of said rst disabling means, said start circuit at said calling station only, and means at the exchange for thereafter controlling said first disabling means to re-enable the start circuits at all of said stations except said calling station.

5. ,In a telephone system, an exchange, a party line outgoing from said exchange, each station on said party line having a rst circuit normally disconnected from said line, a start circuit at each station, a device at each station normally connected to said line over the start circuit thereat, means at each station for transmitting a signal to the exchange over the start circuit at that station when it is desired to extend a call, a switch at each station controlled from the exchange responsive to said signal for opening a point in the start circuit at that station, thereby to disconnect said devices from said line, said switch at the calling station only also controlled from the exchange to connect said device to the line over said first circuit at that station, means at the exchange for thereafter operating said device at the calling station over the line and said first circuit at the calling station, and means controlled by said device upon operation for opening another point in the start circuit at said calling station.

6. In a telephone system, an exchange, a party line outgoing from said exchange, each station on said party line having a first circuit normally disconnected from said line, a start circuit at each station, a device at each station normally connected to said line over the start circuit thereat, means at each station for transmitting a signal to the exchange over the start circuit at that station When it is desired to extend a call, a switch at each station controlled from the exchange responsive t said signal for opening a point in the start circuit at that station, thereby to disconnect said devices from said line, said switch at the calling station only also controlled from the exchange to connect said device to the line over said rst circuit at that station, means at the exchange for thereafter operating said device at the calling station over the line and said rst circuit at the calling station, means controlled by said device upon operation for opening another point in the start circuit at said calling station, and means in the exchange then operated for controlling saidv switches to close said first-named point in the start circuit at each of said stations.

'7. In a telephone system, a party line, a plurality of stations on said line means controlled from any station for extending a call over said line, a start circuit for said means including a portion at each station, means at each station for completing the start circuit portion at that station, means for then disabling the portions at all stations, means for thereafter enabling the start circuit portions, and means at each station controlled over said line to prevent the enabling of any one 01 said portions.

8. In a telephone system, a party line, each station on said line having certain equipment thereat normally disconnected from said line, means operable to cause the equipment at any selected station to be connected to said line, a start circuit at each of said stations for initiating the operation of said means, means for at times disabling said start circuits at all of said stations concurrently, and means operated at other times causing the start circuit at some one of said stations to be disabled without causing the start circuits at the others of said stations to be disabled.

9. In a telephone system, a party line, each station on said line having certain equipment thereat normally disconnected from said line, means operable to cause the equipment at any selected station to be connected to said line, a start circuit at each of said stations for initiating the operation of said means, means for at times disabling said start circuits at all of said stations concurrently and, after an interval, for again enabling them, and means operated at times for preventing said enabling of the start circuit at some one station While permitting said enabling of the start circuits at all other stations.

10. In a telephone system, a party line extending to an exchange, a plurality of stations on said line, means at each station for initiating a call over said line and for locking out all other stations, and means controlled from the exchange over said line and operated whenever a certain station has initiated a call for locking out that particular station and restoring said locked out other stations.

l1. In a system as claimed in claim l0, meam under the control of the subscriber at said particular station for restoring that station after same has been locked out.

l2. In a telephone system, a party line, three or more stations on said line each normally having access to said line for calls, means for associating any one of said stations with said linev to permit that station to engage in a call and, during said call, barring the access of the others of said stations to said line, thereby to prevent said other stations from intruding upon said call, means for at times barring the access of said line of only one of said stations, when no other station on said line is engaged in a call.

13.V In a telephone system, an exchange, a party line outgoing from said exchange, means at the exchange for transmitting particular train of impulses over said line to select different ones of said stations at different times, a switch at the exchange having a wiper operated step-by-step in synchronism with said impulses, and means controlled over said wiper of said switch for insuring that any particular one of said trains c-annot be transmitted under certain conditions.

14. In a telephone system, an exchange, a party line outgoing from said exchange, a register at the exchange operated whenever any station or said line initiates a call, thereby to register the identity of the calling station, and means automatically controlled by said register for permitting calls to be extended over said line, when same is free, only from a predetermined one or more of said stations.

15. In a telephone system, an exchange, a party line outgoing from said exchange, a plurality of stations on said line, means at the exchange for transmitting impulses over said line to select different ones of said stations at different times, a circuit at the exchange including a different portion for each station on said line, a contact in each of said portions operable in different ways independently of the contacts in the others of said portions, a switch at theexchange operated in synchronism with said impulses for rendering the diierent ones of said portions oi ,said circuit effective'in turn, a device in said circuit effective when operated to halt said operation ofsaid impulse transmitting means, and means for operating said device over said cirfor conditioning that station for a call only when said switch has been stepped to a predetermined oi-normal position, the different stations being conditioned at different off-normal positions o1 the respective switches, and means at the exchange responsive to an abnormal condition on said line for causing said rst means to operate said switches to an off-normal position in which no station on said line is conditioned for a call.'

OWEN AVIS PEARCE. 

